How does UR S6 decide the steel grade of a hull plate?

Each structural member is placed in a category (secondary, primary or special) and, by its position along the ship, in material Class I, II or III. Table 7 then gives the lowest grade for that class at the plate's thickness, so a thicker plate or a higher class needs a tougher grade (A, B, D, E). Ships over 150 m and over 250 m get additional minimum grades on key plates.

What changes when a ship operates in cold regions?

For ships operating below −10 °C, plates exposed to the air above the lowest ballast waterline are re-classified under Table 8 and graded by design temperature in Table 9. Design temperature tD is the lowest mean daily average air temperature in the area of operation. Below −55 °C the class society must consider the material specially.

Why does a result read A or AH?

UR S6 gives one grade letter for both series: normal strength (A, B, D, E) and higher strength (AH, DH, EH, FH). You choose the strength level and the sheet appends the strength number, for example DH36. Grade F exists only in the higher-strength series.

Engineering tool

Hull steel grade assignment sheet

List the plates of a ship's hull, give each one its thickness and position, and the sheet returns the minimum steel grade that IACS UR S6 requires. Material class, the thickness table, extra minimums for long ships and low-temperature service are all included.

Ship

Ship length L (m)Ship typeDefault steel strengthDesign temperature tD (°C)

Only for ships operating below −10 °C. tD is the lowest mean daily average air temperature in the area of operation. Leave blank for normal worldwide service.

Hull members

These rows are an example (a 300 m container ship). Edit them, or clear all and enter your own.

Structural memberAs-built thickness (mm)Steel strengthPosition along the ship

In way of an ice-strengthened shell area (Table 6)

Not lower thanEH36Material Class III

How this result was reached

Table 1: member and position give material Class III
Table 7: Class III at 25 mm requires Grade DH
Table 2 (ship over 150 m, single strength deck): not lower than Grade AH within 0.4L
Table 4 (ship over 250 m): not lower than Grade EH within 0.4L
Special member: Class III within 0.4L, Class II outside 0.4L, Class I outside 0.6L (Table 1).

Single strakes required to be Class III (or E/EH, FH) within 0.4L must be at least 1800 mm wide (800 + 5L, not more than 1800 mm), unless the ship's geometry limits it.

Structural memberAs-built thickness (mm)Steel strengthPosition along the ship

In way of an ice-strengthened shell area (Table 6)

Not lower thanAH36Material Class II

How this result was reached

Table 1: member and position give material Class II
Table 7: Class II at 22 mm requires Grade AH
Table 2 (ship over 150 m, single strength deck): not lower than Grade AH within 0.4L
Primary member within 0.4L amidships: Class II (Table 1).

Structural memberAs-built thickness (mm)Steel strengthPosition along the ship

In way of an ice-strengthened shell area (Table 6)

Not lower thanAH36Material Class II

How this result was reached

Table 1: member and position give material Class II
Table 7: Class II at 20 mm requires Grade AH
Primary member within 0.4L amidships: Class II (Table 1).

Structural memberAs-built thickness (mm)Steel strengthPosition along the ship

Within the cargo regionIn way of an ice-strengthened shell area (Table 6)

Not lower thanEH36Material Class III

How this result was reached

Table 1: member and position give material Class III
Table 7: Class III at 32 mm requires Grade EH
Container-ship hatch corner: at least Class III throughout the cargo region (Table 1, C4).

Once you edit the list it is saved in this browser only and is never sent anywhere. “Clear all” removes it.

What this sheet covers

IACS UR S6 Rev.9 Corr.2 for ships of 90 m in length and above: Table 1 (material class by member and position), Table 7 (grade by class and thickness up to 50 mm), Tables 2, 4 and 6 (extra minimum grades for ships over 150 m, over 250 m and ice-strengthened shells), and S6.2 with Tables 8 and 9 (air temperature below −10 °C).

What it does not cover

CSR bulk carriers and oil tankers (UR S6 does not apply to them), membrane-type LNG carriers (Table 3), single-side skin bulk carriers (Table 5), cold cargo (S6.4) and plates over 50 mm. A classification society's own rules can be stricter than the IACS minimum, and the grade on your society-approved drawing always governs.

Common questions

How does UR S6 decide the steel grade of a hull plate?: Each structural member is placed in a category (secondary, primary or special) and, by its position along the ship, in material Class I, II or III. Table 7 then gives the lowest grade for that class at the plate's thickness, so a thicker plate or a higher class needs a tougher grade (A, B, D, E). Ships over 150 m and over 250 m get additional minimum grades on key plates.
What changes when a ship operates in cold regions?: For ships operating below −10 °C, plates exposed to the air above the lowest ballast waterline are re-classified under Table 8 and graded by design temperature in Table 9. Design temperature tD is the lowest mean daily average air temperature in the area of operation. Below −55 °C the class society must consider the material specially.
Why does a result read A or AH?: UR S6 gives one grade letter for both series: normal strength (A, B, D, E) and higher strength (AH, DH, EH, FH). You choose the strength level and the sheet appends the strength number, for example DH36. Grade F exists only in the higher-strength series.

Source

Every table in this sheet was transcribed from IACS Unified Requirement S6 (Rev.9 Corr.2, November 2021) and checked cell by cell against the published page. Table 9 prints one Class III cell as MS = E and HT = FH; it is entered exactly as printed. Original: IACS UR S6 (PDF)

A selection aid, not a class approval. The grades shown are the IACS unified minimum; your classification society's approved plans and rules decide the grade of each plate. Need these plates quoted? Send the list.